The present invention relates to (1) a method for producing a natural rubber master batch and a synthetic isoprene rubber master batch using biodegraded rubber powder and to a rubber composition containing the rubber master batch. The present invention further relates to (2) a method for producing a natural rubber master batch and a synthetic isoprene rubber master batch using rubber powder and a filling agent and to a rubber composition containing the rubber master batch. Further, the present invention relates to a method as a combination of the above methods (1) and (2), which is a method for producing a natural rubber master batch and a synthetic isoprene rubber master batch using biodegraded rubber powder and a filling agent and to a rubber composition containing the rubber master batch.
The rate of collection of waste tires is fairly high as compared to that of common plastic articles, and the collected waste tires are recycled as fuel, particularly in cement plants. However, with increasing awareness of environmental issues, improvement of so-called rate of material recycling is required, that is, recycling of rubber pieces and rubber crumbs produced by chopping off or crushing waste tires. As methods for crushing waste tire, in addition to the roller crush method in which waste tires are crushed mechanically at an ambient temperature, there are the freeze crush method, in which waste tires are frozen by means of e.g. liquid nitrogen and then crushed, and the water hammer crush method with the use of ultra-high pressured water. As described, there are attempts to produce fine particles at low cost.
For the purpose of kneading rubber powder into unvulcanized rubber to produce a vulcanized rubber product, the process of vulcanizing and adhering rubber powder with fresh unvulcanized rubber is important. For example, recycled rubbers have been used since a long time ago, which are produced by mixing a recycling agent and oil with rubber powder, devulcanizing the rubber mixture with heat, and forming it into a sheet-like shape rubber using a roller. Various methods for devulcanizing the surface of rubber powder have been proposed, among which is the crush devulcanization method in which a large shear stress is applied to the rubber powder using e.g. a biaxial extruder. However, there is a disadvantage in these methods of higher energy cost, since a high processing temperature or a high shear stress is required.
Nonpatent Reference 1: Japanese Patent Application Laid-Open H11-236464